Process and product of cold sealing an anodized aluminum article by a photo-polymerization process

ABSTRACT

A method of cold sealing an anodized aluminum article comprising photopolymerizing a cross-linked polymer in situ in the pores of the surface of the anodized layer on the article and the product produced thereby are described.

United States Patent 1191 Quaintance 1 Feb. 6, 1973 54 1 11001353 AND PD COLD 2,552,285 5/1951 Knewstubb et al. .204/351112 SEALING NANOD'IZED'ALUMlNUM 2,893,868 7/1959 Barney ..1 17/9331 UX 2,766,119/1956 Freedman et a1 ..95/8 2,413,973 l/1947 Howk et al. ....1 17/93312,537,433 1/1951 Waring ..204/38 x [75] Inventor: 1 Harold J.Quaintance, Fairview 2,448,513 9/1948 Brennan et al. ..204 3s Park, Ohio3,359,129 12/1967 Mao ..204 159.23 x A 3,426,005 2 1969 S k t l..204/159.22 X [73] Assign: 15 diyisio 3,574,071 411971 ..2 04/38 Searchlncm'pomed 3,418,219 12/1967 Fahlbusch 148/627 x 22 Filed: Feb. 1,1971

Primary ExaminerWi1liam D. Martin [21 1 Appl" L648 AssistantExaminerHarry J. Gwinnell Attorney-Lawrence 1. Field [52] US. Cl..96/35.l 96/86 R, 96/86 P, 96/115 P, 117/75, 117/9331, 117/132 B, [57]ABSTRACT 204/ N, 204/159.23 I 51 Int. Cl .'...G03c 1/94, B32b 15/08 Amemd 9 Sea'mg 94 l 58 Field of Search....204/35 N, 38 A, 38 E, 159.23,C16 'comPflsmg Photopdymemmg ems-Inked 1 204 15922; 117 93 3 132143/627, polymer in situ in the pores of the surface of the 6 1; 96/351R, 86 p 1 5 p anodized layer on the article and the product producedthereby are described. [56] References Cited UN T Q IATEQBATENIL 1 1Claims, N0 Drawings PROCESS AND PRODUCT OF COLD SEALING AN ANODIZEDALUMINUM ARTICLE BY A PHOTO- POLYMERIZATION PROCESS The presentinvention pertains to a novel method of sealing anodized aluminum and tothe product produced thereby. More particularly the invention isdirected to a photosensitive process for producing a polymer within theporous anodized structure which results in an extremely abrasion andchemical resistant product, and which gives the appearance of aconventional hot water seal or nickel/cobalt acetate-hot water seal byvirtue of said polymer filling the pores of an anodized aluminum layer.

As generally used herein, the word aluminum includes aluminum of variousdegrees of purity and various aluminum base alloys. The term anodizedaluminum includes those oxide coatings produced artificially on aluminumas distinguished from the natural oxide films which are normally presenton aluminum surfaces. The present invention is applicable to varioustypes of anodized coatings and has particularly striking advantages whenapplied to anodic coatings produced in electrolytes containing oxalicacid and hereinafter referred to as oxalic acid anodized aluminum.Therefore, the invention will be described in most detail in connectionwith coatings of the type mentioned above.

Anodic oxide coatings are commercially formed on aluminum byelectrolytic action, e.g., as described in a book by S. Wernick and R.Pinner entitled Surface Treatment and Finishing of Aluminum and ItsAlloys, published in 1964 by Robert Draper, Ltd., Teddington, England,and in numerous other texts in this field. Such coatings are superiormechanically and possess greater corrosion resistance than that of thebase metal. The

are not of sufficient size to admit many other materials v of colloidaldispersions and of sufficiently high viscosities. Many clear liquids,such as varnishes, lacquers and liquid polymers, cannot be made topenetrate the anodized porous structure because of this fact and claimsin the literature and prior patents to the effect that such materialspenetrate the pores can be seen to be false upon close examination;where, in fact, it can be seen that only the spongy surface layer of thecoating is penetrated by such materials if there is any appreciablepenetration at all.

Vapors of synthetic resin-forming monomers such as styrene allegedly canbe adsorbed by anodized coatings on aluminum and polymerized therein asdescribed in U.S. Pat. No. 2,662,034, but the product is not acrosslinked polymer and such methods are both time consuming andexpensive to operate.

Dissolved synthetic resin-forming materials can be adsorbed by theanodized coating but this procedure generally requires a long dryingtime to evaporate the excess solvent vehicle before polymerization canproceed unless a heating step is utilized, increasing the cost of theoperation due to the power consumed and in some cases requiring ventingof the heat chamber if flammable or poisonous solvents are expelled. Ifsufficient heat is needed, this may lead to crazing of the anodizedlayer which can occur at temperatures as low as 225F due to thedifferences in coefficients of thermal expansion of the anodized layerand the aluminum substrate.

The anodized coating on aluminum is subject to staining anddiscolorationeffects unless suitably sealed. Therefore, it is common practice to sealthis layer against unwanted staining or discoloration by certainso-called sealing treatments. Commonly practiced sealing techniquesinclude immersion in boiling water or in solutions of dichromates orchromates, silicates, or metal salts such as nickel or cobalt acetateswhich hydrolyze in the coating to form hydroxides. Such treatments areobjectionable because of the long sealing times involved, a tendency insome cases to soften the outer part of the anodized coating whichproduces a chalky surface layer and in the case of dichromates, anundesirable color may be imparted to the coating.

Unsealed oxalic acid anodized aluminum is characterized by a colorranging from silver to bronze, depending on the base metal employed orit may possess a yellow color which in some cases is undesirable andusually is rectified by conventional sealing techniques to produce abright to semiopaque metallic luster. Conventional sealing by waxes,lacquers, varnishes, oils or resins act by imparting a superficialimpervious layer on top of the anodized coating and fail to penetratethe porous structure and fail to mask out the objectionable yellowcolor, and fail to provide an adequate seal against corrosive elementsof the order obtained by conventional hot water or hot water-sealingsalt bath techniques.

The principal object of this invention is to improve the variousproperties of sealed anodized coatings on aluminum.

It is a further object of this invention to provide a method ofimpregnating the pores of anodized aluminum with a photopolymerizablemonomer material which can be polymerized without expensive specialequipment.

It is a further object of this invention to provide a highly abrasionand chemical resistant seal which completely fills the pores of anodizedaluminum, without softening the surface or making it chalky, eliminatingthe need for heat requirements, eliminating the effects of elevatedtemperature crazing on such coatings, and specifically eliminating theobjectional yellow color characteristic of unsealed oxalic acid anodizedaluminum.

It is another object of this invention to provide a method whereby thereis no unreacted by-product or vapor produced either as a result of thereaction or the sealing method employed.

It is another object of this invention to provide a method of sealing ananodized layer at room temperature using an ordinary sunlamp exposureand eliminating the need for a drying period or a heating step.

It is another object of this invention to provide a method of sealing ananodized layer by a photopolymerization process wherein the anodizedpore is completely filled by the polymer material without the presenceof an excess of plastic material on the surface of the anodized layerwhich would in some cases detract from the overall appearance of thefinished product.

The invention has as a particular object the production of anodizedaluminum articles which are impregnated with liquid monomers ordissolved solid monomers, together with a suitable crosslinking agentand the appropriate sensitizers and initiators, exposing saidimpregnated layers to a suitable light source in order to effectphotopolymerization of the monomeric mixture substantially throughoutthe porous structure, in contrast to having a mere overlying surfacecoating of resins or requiring specialized equipment or powerconsumption, as is the case with prior methods.

It is a further object of one aspect of this invention to provide amethod whereby the photopolymerized mixture is crosslinked onlythroughout the porous structure and possibly to some extent on thesurface of the anodized layer, where the excess surface polymer, notbeing crosslinked can be easily removed.

It is a further object of this invention to provide a method whereby theporous anodized structure is completely filled by thephotopolymerized-crosslinked material in contrast to those methodswhereby a low molecular weight material dissolved in a relatively largeamount of solvent is impregnated into the anodized porous layer,resulting in a pore which is relatively unfilled,

It is a further object of this invention to provide a method where, as aresult of the photoinitiated polymerization reaction within the filledanodized porous structure, an improvement in overall appearance inregards to brilliance of the finished article, particularly in regardsto oxalic acid anodized aluminum is obtained as distinguished fromanodized coatings provided with overlying coatings or films of resinousand like substances, such as are obtained with varnishes and lacquers,and as distinguished from high solvent type vehicles containingdissolved resinous substances and the like where an impregnatedsituation may exist but the anodized porous structure remains relativelyunfilled.

It is another object of this invention to provide a method whereby nounreactive components are utilized in the photopolymerization sealingoperation, thereby eliminating the problems associated with heating,solvent removal, and venting considerations.

It is a still further object of this invention to provide a methodwhereby unwanted vapors which are generated, for example, in sealingoperations involving boiling water are eliminated. This aspect will beespecially appreciated by those persons involved in the darkroomprocessing of photographic images embedded in the anodized layer.

Other objects, advantages, and features will become more clearlyapparent from the following description of the invention.

Generally, the invention relates to a novel process for improving theproperties of anodized aluminum by impregnating the pores with aphotopolymerizable monomer or combinations thereof, by a solution ofsolid monomer dissolved in a liquid monomer, or a liquid monomer whichis miscible with a second liquid monomer, or with an aqueous solution orother low boiling point liquid solution which is either a solvent for,or miscible with, a solid monomer or liquid monomer or combinationsthereof, together with a monomer crosslinking agent in the presence of asuitable catalyst and sensitizer, exposing said impregnated layer whilestill wet regardless of the nature of the solvent system employed, to anordinary sunlamp, for example, for a relatively short period of time,which causes a photopolymerization and crosslinking reaction to occur inthe pores of said anodized layer and removing any excess material fromthe surface by means of appropriate solvent or mechanical action.

Any normally liquid to solid photopolymerizable ungroup activated bydirect attachment to a negative group such as halogen,

-C E N, C E C, -O, or aryl. Examples of such photopolymerizableunsaturated organic monomers include acrylamide, acrylic acid,acrylonitrile with acrylamide, acrylonitrile with acrylic acid andacrylamide, acrylamide with acrylic acid, N-ethanol acrylamide,diethylacrylamide, methacrylic acid, calcium acrylate, methacrylamide,vinyl acetate, methylmethacrylate, methylacrylate, ethylacrylate, vinylbenzoate, vinyl pyrrolidone, vinyl methyl ether, vinyl butyl ether,vinylisopropyl ether, vinylbutyrate, butadiene, or mixtures ofethylacrylate with vinyl acetate, acrylonitrile with styrene, butadienewith acrylonitrile and the like.

Difunctional monomers contain two reactive double bonds per molecule,and their use in conjunction with the vinyl monomers serve to radicallyincrease the molecular weight of the polymer and radically alter otherphysical properties of the polymer as well. These compounds serve tocrosslink the polymeric chains and are generally referred to ascrosslinking agents. Among such agents are included compounds such asN,N'- methylenebisacrylamide, triallyl cyanurate, divinyl benzene,divinyl ketones, diglycol diacrylate, diethyl maleate, allylanthranilate, N,N'-hexamethylenebisacrylamide, and ethylenedimethacrylate. Other crosslinking agents suitable for the presentinvention are described in US. Pat. No. 3,330,659. The crosslinkingagent is generally employed in the range of l to 50 parts of the monomerconcentration with 10 parts being generally sufficient to significantlyincrease the molecular weight of the polymer and decrease the solubilityto various solvents.

A monofunctional monomer contains a single reactive double bond permolecule and yields a linear polymer which, in the case of acrylamide,is water soluble. Utilizing a relatively small amount of a difunctionalmonomer with two reactive double bonds per molecule such asN,N-methylenebisacrylamide results in the chains being crosslinked bythe difunctional units to form a vast network which radically alters thephysical properties of the polymer, rendering it insoluble in water andvirtually all common organic solvents. Since liquid acrylonitrile isalso a polymerizable vinyl monomer, capable of crosslinking with N,N'-methylenebisacrylamide, a solvent is provided, for the crosslinkingagent and acrylamide monomer which in itself becomes a part of thefinished product and eliminates the problems associated with dryingtimes and solvent evaporation and removal. In addition, such a systemgoes into the pores of anodized aluminum quite easily and with theneeded sensitizers to ultraviolet light can be polymerized in situ,assuring an effective seal and eliminating the objectionable colorcharacteristic of oxalic acid anodized aluminum by virtue of the poresbeing filled.

This method has the decided advantage over other cold sealing techniquesin that a solvent is generally used with the dissolved polymer which asa rule requires heat to drive off excess solvent or to effectcrosslinking or film formation or both. Inasmuch as a relatively largeamount of solvent is required in order to obtain sufficiently fluidviscosity in order to penetrate the pores, this situation may seal theanodized layer but will not mask out the objectionable color or give theappearance of a normal hot water seal. Unless thicker layers areapplied, the pore will not be filled and complete sealing may not occur.On the other hand, if excess solution is applied, a film may be left onthe surface of the anodized layer and although sealed, an obviousplastic layer detracts in some cases from the finished appearance of themetal. To avoid this situation, the conventional cold sealing materialwould have to be carefully metered on, being subject to the variety ofdifferent anodized thicknesses as well as the porosity of the anodizedlayer, or the excess removed after curing.

In the photopolymerization cold sealing technique, all problemsassociated with excess solvent are eliminated since the solvent in thiscase is a vinyl monomer which enters into the polymerization reactionitself. Secondly, the technique can be tailored to the extent thatcrosslinking takes place only in the pore of the anodized layer andpossibly to some extent on the surface as well. The excess surfacematerial which has not been crosslinked can be removed in an appropriatesolvent or by a mechanical action, leaving the crosslinked portion ofthe sealer unaffected within the anodized porous layer.

In photopolymerization, photochemical reactions initiate a series ofreactions in which many small monomer molecules combine -to form longpolymer chains. Most practical monomers have the general molecularstructure where either one or both of X and X are electron withdrawingsubstituents that activate the adjacent double bond. Photopolymerizationof such monomers can proceed only when an initiator is present in thesystem. An initiator can be either a monomer molecule that has receivedenough energy to combine with another monomer molecule or, morecommonly, an initiator can be a different material which is more easilyactivated than the monomer. The activation takes place through theabsorption of energy; in this case light quanta which is then dissipatedthroughout the substance to produce a short lived intermediate known asa free radical. An impressive number of compounds useful asphotoinitiators and/or sensitizers have been reported in the literatureand their choice depends on the particular monomer employed as well asthe nature of the light source used to initiate photopolymerization.Among these are the broad class of carbonyls such as diacetal, benzil,or benzoin and its congeners, the acyloins such as a-alkylbenzoin;benzophenone or substituted benzophenones such as4,4-bisdimethylaminobenzophenone, known as Michlers ketone"; organicsulfur-containing compounds such as diphenyl disulfide; peroxidecompounds such as ditertbutyl peroxide or benzoyl peroxide; redoxsystems, for example organic peroxides in the presence of certainreducing agents such as ferric compounds such as ferric ammoniumoxalate; azo and diazo compounds such as azomethane or the diazoniumchloride of paminodiphenylamine; organic halogen compounds such asa-chloromethylnaphthalene; organic halogen sulfur-containing compoundssuch as benzene sulfonyl chloride; certain photoreducible dyes such asrose bengal or acriflavine and in conjunction with reducing agents suchas stannous chloride, or ascorbic acid; etc. A more complete listing ofthe various combinations of sensitizers and catalysts which can be usedin the spirit of this invention is described by Jaromir Kosar, LightSensitive Systems 5, John Wiley and Sons (l965).) and are known in theart.

The nature of the light source used to effect photopolymerization willdepend on the sensitizer or sensitizer-catalyst combination employed.While ultraviolet light sources are generally the most efficient forinitiating a photopolymerization reaction by using certainphotoreducible dyes and reducing agents and combinations thereof, thelight source can be extended through the entire visible portion of thespectrum. X- rays or gamma rays could also be used.

The advantages of this invention will be made further apparent by thefollowing examples; although, it is to be understood that the inventionis not restricted thereto.

EXAMPLE 1 A composition was prepared from the following components:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 gBenzoyl peroxide 0.15 g Acrylonitrile cc The resulting solution wascoated on an oxalic acid anodized aluminum plate and immediately exposedto a General Electric RS 275 watt sunlamp placed at a distance of 12inches. Within to minutes exposure a solid polymeric surface film hadformed which, when removed, left an anodized layer of high gloss andbrilliance which was sealed against staining. An identical untreatedoxalic acid anodized aluminum plate was characterized by a yellowcoloration and would very strongly accept staining by dyes, indicatingpore penetration had occurred on the above treated plate. Additionalplates prepared by the same method have been immersed in water, methylethyl ketone, acrylonitrile, trichloroethylene and isopropyl alcohol forperiods of up to 6 weeks. The anodized layer was unchanged in appearanceand still was sealed against staining.

The above solution was coated onto an oxalic acid anodized aluminumarticle, whose anodized layer contained a fully developed and fixedsilver image produced as described in US. Pat. No. 2,766,119, forexample. The article was exposed and treated in the same manner asbefore. The resulting article is characterized by an improved gloss andbrilliance in the nonimage area and an improved density and blackness inthe image area as compared to a conventional hot water seal or combinedhot water-sealing salt additive bath. The integrity of the seal wasverified by placing a drop of iodine-potassium iodide mixture dissolvedin methanol on an image area of the anodized layer. No fading wasapparent after the so-treated area was allowed to set for severalminutes. An unsealed imaged plate so treated with iodine will fade inseveral seconds under the same conditions.

EXAMPLE 2 A composition having the following components was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 gBenzoyl peroxide 0.15 g Acrylic acid 7 cc Acrylonitrile 100 cc Theresulting solution was coated onto an oxalic acid anodized aluminumarticle and exposed to a General Electric RS 275 watt sunlamp placed ata distance of 12 inches from the article for a period of minutes. Theresulting excess resinous surface film was removed, leaving a highlybrilliant glossy surface as obtained in Example 1.

EXAMPLE 3 A composition of the following components was prepared:

Acrylamide 30 g N,N'-methylenebisacrylamide 3 g Benzophenone 0.3 gBenzoyl peroxide 0.15 g Methylmethacrylate 7 cc Acrylonitrile 100 ccThis composition was applied the same as in Example 1 and essentiallythe same results were obtained.

EXAMPLE 4 The following composition was prepared:

Acrylamide 30 g N,N'-methylenebisacry1amide 3 g Benzophenone 0.3 gBenzoyl peroxide 0.15 g Acrylic acid cc Methylmethacrylate 10 ccAcrylonitrile 100 cc The resulting solution was applied to an oxalicacid anodized aluminum plate and treated as before. Again a 20 minuteexposure was required.

EXAMPLE 5 The following two compositions were prepared from theindicated components:

Solution A N,N'-methylenebisacry1amide Benzophenone Benzoyl peroxideAcrylonitrile Solution B Acrylamide N,N'-methylenebisacrylamideBenzophenone Benzoyl peroxide Acrylonitrile Solution A was coated ontoan oxalic acid anodized aluminum article within which anodized layer afully developed and fixed silver image was present. The excess solutionwas then poured off and Solution B applied in excess and exposed asbefore. Polymerization was essentially complete in 5 minutes after whichthe excess surface film was easily removed by a light scrubbing actionunder running tap water since the excess surface polymer is essentiallynot crosslinked to yield an exceptionally bright, glossy surfaceappearance which again passed the iodine-potassium iodide-methanolsealing test in addition to satisfying an abrasion test conducted with aTabor abrader, which satisfies the requirements outlined under Mil.Spec. GGP-455-b.

EXAMPLE 6 A composition having the following components was prepared:

Acrylamide 37 g N,Nmethy1enebisacrylamide 2 g Benzophenone 0.3 g Benzoylperoxide 0.15 g Ethyl alcohol 100 cc The resulting solution was coatedonto an oxalic acid anodized aluminum plate and immediately exposed to a275 watt General Electric RS sunlamp placed at a distance of 12 inchesfor a period of 7 minutes. Essentially the same result was obtained asin Example 1'.

EXAMPLE 7 A composition of the followingcomponents was prepared asfollows:

Acrylamide 30 g N.N'-methylenebisacrylamide 3 g Benzophenone 0.3 gBenzoyl peroxide 0.15 g Acetonitrile 100 c The solution was coated ontoan oxalic acid anodized aluminum plate and immediately placed under aGeneral Electric RS 275 watt sunlamp placed at a distance of 12 inchesfor a period of 10 minutes after which the coating had polymerized. Theexcess surface polymer was removed, resulting in a sealed anodizedsurface comparable to that obtained in Example 1.

EXAMPLE 8 A composition consisting of the following components wasprepared:

Acrylamide 100 g N,N-methylenebisacrylamide 5 g Benzophenone l g Benzoylperoxide (dissolved in ethanol) 0.5 g Water (distilled) 100 cc It wasnecessary to dissolve the peroxide in ethanol in order to incorporate itinto the above solution. The above composition when coated onto anoxalic acid anodized layer required 20 minutes of exposure to theprevious mentioned light source. The resulting impregnated polymerizedlayer was sealed as before with regards to abrasion and staining tests.

EXAMPLE 9 A composition of the following components was prepared:

Acrylamide I g N,N-methylenebisacrylamide g Ferric ammonium oxalate l gHydrogen peroxide (3% aqueous solution) 5 cc Water lOO cc The resultingsolution was coated onto an oxalic acid anodized plate and immediatelyexposed to the 275 watt sunlamp at a distance of 12 inches. Within 1 to2 minutes, a solid polymeric surface film was obtained which, whenremoved, resulted in an anodized layer of high glossand brilliance whichwas sealed against stainmg.

EXAMPLE The following two compositions were prepared from the indicatedcomponents:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 gHydrogen peroxide (3% aqueous solution) 2 cc Methyl alcohol 75 cc \Vater(distilled) cc Solution B Acrylamide 100 g Water (distilled) I00 ccSolution A was coated onto an oxalic acid anodized aluminum layer andallowed to set for 1 minute and the excess poured off. Solution B wasthen applied and the impregnated anodized layer immediately exposed tothe General Electric RS 275 watt sunlamp placed at a distance of 12inches. A clear, amorphous, solid surface film had formed in 1 minutewhich, when removed, resulted again in an anodized layer of high glossand brilliance, with no evidence of the yellow color characteristic ofthe unsealed layer and which would not accept a dye. Essentially thesame result was obtained by adding 5% N,N-methylenebisacrylamide toSolution B. The same result was also obtained by combining Solution Aand B in equal amounts and applying this combined mixture to an oxalicacid anodized layer.

EXAMPLE 1 l A composition was prepared where the coating solutionconsisted of the following components:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 gHydrogen peroxide (3% aqueous solution) 2 cc Methyl alcohol cc Water(distilled) 25 cc Solution B Acrylamide l00 g Methyl alcohol 150 cc Theresults were the same as obtained in Example 1 except the time ofexposure required to effect polymerization was increased to 5 minutes.

EXAMPLE 12 The following two compositions were prepared accordingly:

Solution A N,N'-methylenebisacrylamide 4 g Ferric ammonium oxalate 0.2 gHydrogen peroxide (3% aqueous) 2 cc Methyl alcohol 75 cc Water(distilled) 25 cc Solution B Acryalmide 25 g Acrylonitrile cc Solution Awas coated onto an oxalic acid anodized aluminum plate and allowed toset for 1 minute and the excess poured off. Solution B was then appliedand the impregnated layer immediately exposed to the General Electric RS275 watt sunlamp placed at a distance of 12 inches from the plate. Theresults were the same as obtained in Example 10, except l0 minutesexposure time was required to effect polymerization.

A 5% N,N-methylenebisacrylamide addition to Solution B or combiningSolution A and B in a 1:1 volume ratio gave essentially the same result.

EXAMPLE 13 A composition of the following indicated components wasprepared:

Acrylamide 30 g N,N-methylenebisacrylamide 3 g Ferric ammonium oxalate(0.01M) 5 cc Hydrogen peroxide (3% aqueous) 0.5 cc Methanol 35 cc Water(distilled) 25 cc The resulting solution was coated onto an oxalic acidanodized aluminum article and exposed for 3 minutes with a GeneralElectric RS 275 watt sunlamp placed at a distance of 12 inches from thearticle to effect polymerization. The clear, amorphous, excess surfacefilm was removed leaving a bright, glossy anodized surface appearancewith no evidence of the characteristic unsealed yellow coloration andresisted staining or coloring.

EXAMPLE l4 A composition was prepared from the following indicatedcomponents:

Acrylamide 7 g N,N-methylenebisacrylamide 0.7 g Ferric ammonium oxalate(0.01M) l.0 cc Hydrogen peroxide (3% aqueous) 0.1 cc Methanol 6 cc Water4 cc Acrylonitrile l cc This composition when coated onto an oxalic acidanodized aluminum article and exposed for 3 minutes resulted in anespecially brilliant, glossy appearance when the excess surface polymerwas removed.

EXAMPLE 15 A composition was prepared from the indicated components:

Acrylamide 100 g N,N'-methylenebisacrylamide 5 g Ferric ammonium oxalate(0.0lM) 5 cc Hydrogen peroxide (3% aqueous) 3 cc Sodium tetradecylsulfate 02 cc Water 100 cc The resulting solution was coated onto anoxalic acid anodized aluminum article and allowed to set for 5 minutesprior to exposure. The degree of gloss and brilliance obtained issomewhat improved over that obtained in Example 9.

EXAMPLE 16 The following composition was prepared:

Acrylamide 20 g N,N'-methylenebisacrylamide 4.5 g Acrylonitrile 50 ccAcrylic acid 5 cc Hydrogen peroxide (3% aqueous) cc Ferric ammoniumoxalate (0.01 M) l0 cc Methanol l0 cc This composition, when coated ontoan oxalic acid anodized aluminum article, polymerizes to a film in 5minutes when placed at a distance of 12 inches from a 275 watt sunlamp.The degree of gloss is approximately the same as obtained in Example 15when the excess surface polymer is removed.

EXAMPLE 17 A composition of the following indicated components wasprepared:

Acrylamide 20 g N,N'-meth lenebisacrylamide 4.5 g Acrylonitri e 50 ccAcrylic acid 5 cc Hydrogen peroxide (3% aqueous) l0 cc Ferric ammoniumoxalate (0.lM) 10 cc Methanol l0 cc Water (distilled) 20 cc Thiscomposition gave essentially the same result as obtained in Example 16,except the coating polymerized in l to 2 minutes under the same exposureconditions EXAMPLE 18 The following composition was prepared:

Acrylic acid 50 cc N,N'-methylenebisacrylamide 10 g Hydrogen peroxide(3% aqueous) 5 cc Ferric ammonium oxalate (0.01M) 5 cc This composition,when coated onto an oxalic acid anodized aluminum plate and immediatelyexposed to the aforementioned light source, polymerized in 2 minutes toa particularly hard, resistant coating which, when removed, resulted ina clear, non-yellow, stain resistant anodized layer.

EXAMPLE 1) The following composition was prepared from the indicatedcomponents:

Acrylic acid 50 cc Methylmethacrylate 20 cc N,N'-methylenebisacrylamide2 g Hydrogen peroxide 5 cc Ferric ammonium oxalate 5 cc This coatingyields essentially the same results obtained in Example 18, except thata 5 minute exposure was used.

EXAMPLE 20 A composition having the following components was prepared:

Acrylamide g N,N'-methylenebisacrylamide 3.5 g Acrylic acid 40 ccAcrylonitrile cc Hydrogen peroxide (3% aqueous) l0 cc Ferric ammoniumoxalate (0.01M) 10 cc Sodium tetradecyl sulfate 0.2 cc Water 60 cc Thiscomposition, when coated onto an oxalic acid anodized article, resultedin a plate with about the same final appearance as obtained in Example5. The polymerization exposure time was reduced to 1 minute however. Theabove composition was also coated onto an oxalic acid anodized aluminumarticle within which a fully developed and fixed silver image waspresent. The resulting article is characterized by an improved gloss andbrilliance in both the image and nonimage area as well as a more neutralblack coloration in the image area as compared to an equivalent articlewhich was sealed in a boiling water-nickel-cobalt acetate sealing bath.The integrity of the above sealed material was confirmed by themethanol-potassium iodide-iodine bleaching test in the silver image areaand the nonimage area would not accept a dye.

EXAMPLE 21 A composition of the following components was prepared:

Acrylamide 25 g N-vinylpyrolidone 2.5 g N,N'-methylenebisacrylamide 2.5g Benzophenone 0.5 g Benzoyl peroxide 0.25 g Acrylonitrile lOO cc Anexcess solution was coated onto an oxalic acid anodized aluminum articleand exposed immediately to a General Electric RS 275 watt sunlamp placedat a distance of 12 inches for a period of 2 minutes. When the excesssurface coating was removed, a glossy,

highly reflectant surface was noted similar to that obtained in Example1.

EXAMPLE 22 A composition consisting of the following indicatedcomponents was prepared:

Acrylamide 25 g Diethyl maleate 2.5 g Acrylonitrile 100 cc Benzophenone0.5 g Benzoyl peroxide 0.25 g

An oxalic acid anodized aluminum plate was coated with this formulationand immediately exposed to the sunlamp for minutes after which theexcess coating was removed, providing a highly brilliant surfaceappearance with no characteristic yellow color which is evident on anunsealed oxalic acid anodized aluminum surface.

EXAMPLE 23 A composition consisting of the following components wasprepared:

Acrylamide 25 g Allylanthranilate 2.5 g Benzophenone 0.5 g Benzoylperoxide 0.25 g Acrylonitrile 100 cc Essentially the same result wasobtained as in Example 1, except a 2 minute exposure time was utilized.

EXAMPLE 24 A solution consisting of the following indicated componentswas prepared:

Acrylamide 25 g Ethylene dimethacrylate 2.5 g Benzophenone 0.5 g Benzoylperoxide 0.25 g Acrylonitrile 100 cc The resulting solution was coatedonto an oxalic acid anodized aluminum article which was characterized bya very strongly objectionable yellow color appearance and exposed to the275 watt sunlamp for 3 minutes. After the excess surface polymer wasremoved a brilliant, highly reflectant, glossy surface was obtained,similar to that obtained in Example 1.

EXAMPLE 25 A composition of the following indicated components wasprepared:

Aerylamide 25 g N,N'-hexamcthylenebisacrylamide 2.5 g Benzophenone 0.5 gBenzoyl peroxide 0.25 g Acrylonitrile 100 cc The resulting solution wascoated onto an oxalic acid anodized aluminum article and exposed for aperiod of 4 minutes with a General Electric RS 275 watt sunlamp placedat a distance of 12 inches from the article in order to effectpolymerization. The surface polymeric film was removed, leaving abright, glossy anodized surface appearance with no evidence of thecharacteristic unsealed yellow coloration and which would not accept adye or stain.

EXAMPLE 26 5 A composition having the following indicated components wasprepared:

Acrylamide 90 g N,N-hexamethylenebisacrylamide 3.5 g Acrylic acid 40 ccAcrylonitrile 100 cc Hydrogen peroxide (3% aqueous) 10 cc Ferricammonium oxalate (0.01M) l0 cc Water (distilled) 60 cc This composition,when coated onto an oxalic acid anodized article, polymerizes to a filmin 1 to 2 minutes when placed at a distance of 12 inches from a 27 5watt sunlamp. The resulting surface film was removed, leaving a surfaceappearance similar to that obtained in Example 25 and which resistedstaining.

EXAMPLE 27 A monomer solution was prepared from the following indicatedcomponents:

Styrene 70 cc Acrylonitrile 30 cc N,N'-methylenebisacrylamide 2 gBenzophenone 0.5 g 30 Benzoyl peroxide 0.25 g

This composition, when coated onto an unsealed oxalic acid anodizedaluminum article and exposed for 2 to 3 minutes, resulted in abrilliant, glossy surface. appearance when the excess surface polymerwas removed.

EXAMPLE 28 40 The following composition was prepared:

The following composition was prepared:

Styrene 100 cc Maleic anhydride 25 g N,N'-methylenebisacrylamide 5 gBenzophenone 0.5 g Benzoyl peroxide 0.25 g

EXAMPLE 29 A composition having the following components was prepared:

Styrene 60 cc Maleic anhydride 25 g Acrylonitrile 40 cc 5N,N'-methylenebisacrylamide 5 g Benzophenone 0.5 g Benzoyl peroxide 0.25g

The above composition was coated onto an oxalic acid anodized aluminumarticle within which a fully developed silver image was embedded. Anexposure time of 2 minutes was deemed sufficient to photopolymerize andcrosslink the excess surface film at a distance of 12 inches from theGeneral Electric RS 275 watt sunlamp. The resulting excess surface filmwas removed leaving an improved gloss and brilliance in the nonimagearea as well as an improved apparent density and blackness in the imagearea, as compared to that obtained by a conventional hot water-sealingsalt bath technique. The developed silver image area would not fadegiven the iodine-potassium iodidemethanol test and the nonimage area ofthe anodized layer would not accept staining.

1 claim:

1. A method of improving the properties of an anodized aluminum articlewhich comprises:

applying to the porous surface of an unsealed anodized aluminum layer aphotopolymerizable liquid composition comprising at least onepolymerizable acrylic monomer, and at least one crosslinking agent; and

cold sealing the porous surface of said article by ex posing saidcomposition to a suitable dose of radiation thereby photopolymerizingthe composition in the pores of the surface of said article.

2. The method of claim 1 wherein the anodized article contains adeveloped and fixed silver image in the pores of said article prior toapplication of said polymerizable composition.

3. The method of claim 1 wherein the crosslinking agent is adifunctional monomer.

4. The method of claim 1 wherein the polymerizable composition alsoincludes a sensitizer or initiator.

5. The method of claim 1 wherein photopolymerization is the result ofexposure to ultra violet radiation.

6. The method of claim 1 wherein the photopolymerizable compositioncomprises acrylamide, N,N'-methylenebisacrylamide and a solvent for saidacrylamides.

7. A cold sealed anodized article in which the pores of the porousanodized surface layer are filled with a cross-linked copolymer of atleast one photopolymerizable acrylic monomer and at least onecross-linking agent.

8. A cold sealed anodized article according to claim 7 in which thephotopolymerizable monomer impregnated in the pores is a mixture ofacrylamides and acrylonitrile.

9. A cold sealed anodized article according to claim 7 in which adeveloped and fixed silver image is in the pores along with thecrosslinked copolymer.

10. A cold sealed anodized article according to claim 1 7 in which thecrosslinked polymer is a copolymer of at least one acrylic monomer and adifunctional crosslinking agent.

11. The article of claim 7 wherein the crosslinked copolymer is acopolymer of acrylamide and N,N'- methylenebisacrylamide.

1. A method of improving the properties of an anodized aluminum articlewhich comprises: applying to the porous surface of an unsealed anodizedaluminum layer a photopolymerizable liquid composition comprising atleast one polymerizable acrylic monomer, and at least one crosslinkingagent; and cold sealing the porous surface of said article by exposingsaid composition to a suitable dose of radiation therebyphotopolymerizing the composition in the pores of the surface of saidarticle.
 2. The method of claim 1 wherein the anodized article containsa developed and fixed silver image in the pores of said article prior toapplication of said polymerizable composition.
 3. The method of claim 1wherein the crosslinking agent is a difunctional monomer.
 4. The methodof claim 1 wherein the polymerizable composition also includes asensitizer or initiator.
 5. The method of claim 1 whereinphotopolymerization is the result of exposure to ultra violet radiation.6. The method of claim 1 wherein the photopolymerizable compositioncomprises acrylamide, N,N''-methylenebisacrylamide and a solvent forsaid acrylamides.
 7. A cold sealed anodized article in which the poresof the porous anodized surface layer are filled with a cross-linkedcopolymer of at least one photopolymerizable acrylic monomer and atleast one cross-linking agent.
 8. A cold sealed anodized articleaccording to claim 7 in which the photopolymerizable monomer impregnatedin the pores is a mixture of acrylamides and acrylonitrile.
 9. A coldsealed anodized article according to claim 7 in which a developed andfixed silver image is in the pores along with the crosslinked copolymer.10. A cold Sealed anodized article according to claim 7 in which thecrosslinked polymer is a copolymer of at least one acrylic monomer and adifunctional crosslinking agent.